This invention is related to the foaming and crosslinking of elastomeric and/or thermoplastic polymers at elevated temperatures using a t-alkylhydrazinium salt or a carbonylhydrazine with a free radical initiator.
Prior to the present invention there existed the need to balance the decomposition of the blowing agent to the decomposition of the initiator in order to obtain good quality crosslinked foamed products using the prior art organic peroxide initiators and chemical blowing agents systems for crosslinking and foaming elastomeric or thermoplastic polymers. If this balance is not maintained, a significant amount of the initiator may decompose prior to gas generation from the blowing agent, thus generally producing a product with very little foaming having coarse and nonuniform cell size. If the blowing agent significantly decomposes prior to the initiator decomposition, on the other hand, the resulting product will have a collapsed foam structure. In the prior art systems both the crosslinking agent and blowing agent functioned independently.
The foaming and crosslinking (or curing) of polymeric resins are well known in the prior art. U.S. Pat. No. 4,393,148 discloses the foaming and curing of an unsaturated polyester resin at ambient temperatures using a peroxide curing agent, an iron or copper metal salt promoter, and a t-alkylhydrazinium salt as a blowing agent. U.S. Pat. No. 4,435,525 discloses the foaming and curing of an unsaturated polyester resin at ambient temperatures using a peroxide curing agent, an iron or copper metal salt promoter, and a carbonylhydrazine as a blowing agent. Published European patent application no. 0048050 discloses the foaming and curing of an unsaturated polyester resin using a peroxide curing agent, an organometallic salt promoter, and a t-alkylhydrazine blowing agent. None of these references discloses the present invention.